Electric motors are currently known which comprise a containment shell for a road tour, which is closed by a cover provided with a hole for the passage of the motor shaft.
The cover accommodates and supports brushes for sliding contact on a commutator for supplying power to the rotor, a sensor for detecting the rotation rate of said rotor, generally of the Hall-effect type, and connections for transmitting signals and for supplying power to said sensor.
The Hall-effect sensor is suitable to detect the passage in front of it of the poles of a magnet that is rigidly coupled to the motor shaft.
Electric motors in which the sensor is installed in the cover or on an equivalent similar flange that supports the brushes are much more compact than electric motors provided with a Hall-effect sensor installed in appropriate additional recesses.
Such additional recesses in fact increase the overall dimensions of the motor; moreover, in view of the particular arrangement of the magnet at a distance from the sensor, these constructive solutions require larger and heavier rotor magnets, with disadvantages in terms of costs, shaft rotation balancing and motor efficiency.
Such electric motors, in which the sensor is installed in the cover or on an equivalent similar flange that supports the brushes, are very compact and can be fitted with relatively small magnets, and although solving the drawbacks exhibited by known electric motors with a Hall-effect rotation rate sensor, have aspects that can be improved.
The fitting of the transmission and power supply connections of said sensor, and the fitting of the power supply lines for any other additional components (such as passive components for the signal line and/or filtering components for supplying power to the rotor), in fact requires welding or soldering operations.
These operations entail the onset of mechanical stresses between the connections and the power supply lines and the corresponding seats, and such stresses may compromise the efficiency of the junctions to the external lines.
Further, said Hall-effect sensors are often rigidly coupled to a printed circuit, which in turn has to be inserted in a suitable receptacle inside the brush supporting cover (or flange).
Such printed circuit, too, is subjected to welding operations.
The printed circuit, which is a rigid body, is suitable to interface with other bodies for example by means of four or six power supply lines.
Therefore, the welding operations entail, for the printed circuit, the triggering of mechanical stresses both during assembly, caused by the dimensional quality of said circuit and of the electrical junctions connected thereto, and after assembly, due to the subsequent handling processes or to the vibrations of the machine in which the electric motor is installed.
These mechanical stresses can lead to damage to the electrical junctions and to the consequent lack of electrical continuity.